StarDate Podcast

An astronomical trio lines up low in the east at first light tomorrow. Two of its members are easy to pick out: Venus, the brilliant “morning star,” with the true star Aldebaran close to its right. But to see the third member, you need to pull out your binoculars. NGC 1647 is just to the right of Venus, much closer than Aldebaran is. It’s a star cluster – a tightly packed family of hundreds of stars. Most of the cluster’s details are a bit fuzzy, though. Estimates of its age, distance, and the number of stars vary by quite a bit. In part, that’s because the cluster is behind a cloud of dust, which absorbs some of its light. But it’s also because NGC 1647 hasn’t received a lot of attention. Measurements put the cluster’s distance at about 1800 to 2,000 light-years. One study said the cluster has at least 600 member stars, while another puts the number at 1300 or more. And estimates of its age range from about 120 million years to more than 260 million. Based on the structure of NGC 1647, it appears that no matter how old it is, it may not last much longer. The cluster may be losing its grip on the stars outside its dense core. The stars are being pulled away by the gravitational tug of the rest of the galaxy. Soon, many of them could drift away – leaving a much smaller family of stars. Tomorrow: shaking hands. Script by Damond Benningfield

If you ever find yourself floating above the clouds of Saturn, gazing upon the planet’s magnificent rings, you might feel like you need to get your eyes checked. Even at noon, when the Sun is highest in the sky, the view will look as dim as the minutes before sunrise or after sunset here on Earth. That’s because Saturn is almost 10 times farther from the Sun than Earth is. At that distance, the Sun shines only about one percent as bright as it does on Earth. And that presents some problems for spacecraft that travel to Saturn. For one thing, they can’t use solar power. They’d need huge arrays of solar cells, which would make a craft far too heavy and expensive. Instead, Saturn-bound missions are nuclear powered. For another, it’s hard to take good pictures. A craft has to leave the shutter open for a long time to properly expose an image. At the speeds a craft is moving, that blurs the shot. The solution is to turn either the camera or the entire spacecraft to stay focused on the target. No spacecraft are operating at Saturn now. The next one is scheduled for launch in a few years. It’ll ferry a small helicopter to Saturn’s big moon Titan – under the faint light of the distant Sun. Saturn appears near our own Moon early tomorrow. It looks like a bright star, standing just below the Moon at dawn. The planet fades from view as the sky brightens – under the full glory of the nearby Sun. Script by Damond Benningfield

Only about one in five Americans was born before the “Mars Era” – before the first spacecraft visited the Red Planet. That first encounter took place 60 years ago today, beginning six decades of Mars exploration. Mariner 4 was launched in late 1964. A sister craft had failed. And early Soviet efforts failed as well. That inspired jokes about a “great galactic ghoul” eating Mars-bound probes. Mariner 4 had eluded the ghoul for seven months. AUDIO: Then, July 14th: Encounter Day. This is Mariner control. All systems are green. And as this NASA film explained, they stayed green. AUDIO: The shutter is operating, the TV sees the planet, the recorder is working. Mariner skimmed just 6100 miles from Mars. It snapped 21 pictures. The images depicted a landscape of craters and volcanic plains. They made Mars look like a dead planet. Yet Mars exploration continued. Later missions revealed that Mariner 4 was unlucky – it scanned an unusually desolate strip. Today, we know that Mars has an active atmosphere. Ice lurks just below its surface. And it once was warm and wet, with rivers flowing across its surface, perhaps filling a giant ocean – making Mars a possible home for life. Today, a half-dozen orbiters and rovers are exploring the planet. And others are being planned – extending a legacy of exploration that began six decades ago. Script by Damond Benningfield

A brilliant “new” star blazed into view more than a thousand years ago. It’s the brightest star ever recorded, and may be the brightest ever seen by human eyes. Supernova 1006 first appeared in late April of the year 1006. For a few weeks it shined many times brighter than Venus, which is the brightest object in the night sky after the Moon. It was bright enough to see during the day, and remained visible at night for more than two years. It was recorded by cultures around the world. At the time, nobody knew what the star actually was. Today, though, we know it was a supernova. It formed in a binary system. At least one of the two stars was a white dwarf – a stellar corpse. It might have pulled gas from a living companion star. Or perhaps the companion was another white dwarf, and the two stars rammed together. Either way, a white dwarf was pushed beyond its critical weight limit. That caused a runaway nuclear explosion that blasted the star to bits. Debris from the blast continues to race outward at millions of miles per hour. Astronomers watch this debris, mainly in radio waves and X-rays, to learn more about the star and its demise. Supernova 1006 was along the border between the constellations Lupus and Centaurus. The spot is low in the south-southwest at nightfall. But the residue of this brilliant outburst has faded away. Large telescopes reveal only a colorful ribbon at the edge of the expanding bubble. Script by Damond Benningfield

A couple of bright cousins of Antares, the heart of the scorpion, skitter to its lower right on July evenings. They’re the brightest stars of Lupus, the wolf. The stars of Lupus originally formed part of the adjoining constellation Centaurus. But they were split off to form a new constellation a couple of thousand years ago. The wolf’s brightest stars are Alpha and Beta Lupi. Both stars belong to the Scorpius-Centaurus O-B association – a complex of stars and star-making ingredients that spans hundreds of light-years. The first stars in the association were born about 25 million years ago. Beta Lupi probably was one of those stars. Winds from the earliest stars, along with shockwaves from exploding stars, probably triggered a major round of starbirth about five million years later. And two more big rounds followed, spaced about five million years apart. Alpha Lupi probably was born during one of those peaks, no more than 20 million years ago. Alpha Lupi is about 10 times the mass of the Sun. So despite its young age, it’s nearing the end. It will explode as a supernova within the next few million years. Beta Lupi is a little less massive. So it might explode as well. But it’s possible that it faces a less dramatic fate, ending its life as a small, faint ember – a meek end for a mighty star. Lupus is quite low in the south at nightfall. You need to be south of about Dallas or Phoenix to see its brightest stars. More about the wolf tomorrow. Script by Damond Benningfield

Newly forming planetary systems are busy and messy. They contain disks of gas, ice, and dust that are broken into wide bands. The supply of dust is replenished by frequent collisions between “exocomets” – balls of ice and rock up to a few miles across. And the bands may be stirred by the back-and-forth shifting of newborn planets. There’s a similar band in our own solar system – the Kuiper Belt. It begins beyond the edge of Neptune, the outermost major planet, and extends billions of miles from the Sun. Because the solar system has been around for billions of years, the belt is quiet – there are few collisions and little stirring. Astronomers recently studied the bands in about 300 young star systems. They contain a lot of leftover debris from the birth of the planets. So collisions between larger bodies are much more frequent. The impacts blast out a lot of dust, feeding the bands. In many systems, there’s more than one band. Gaps between them might have been cleared out by orbiting planets. And the bands come in different sizes. Wider ones might have been “pumped up” as giant planets moved toward and away from the parent star. The gravity of those planets would have kicked many of the exocomets into different orbits, causing them to spread out. The study didn’t see any planets. But the configurations of the bands suggest the planets are there – taking shape in the busy space around young stars. Script by Damond Benningfield

When it comes to the night sky, what you see isn’t necessarily what you get. Consider Venus and Aldebaran, which are low in the east at first light. Venus is the brilliant “morning star.” Aldebaran stands directly below Venus, and shines just one percent as bright. But their apparent brightness is the only way in which Venus outranks Aldebaran. Venus is a planet in our own solar system – a little smaller and less massive than Earth. It’s so brilliant because it’s close to both Earth and the Sun, and because it’s covered in bright clouds. Aldebaran, on the other hand, is a true star – and an impressive one at that. It’s heavier than the Sun, about 45 times wider, and more than 400 times brighter. Compared to that, Venus is a bare speck – a flake of cosmic jetsam. Aldebaran is almost half a million times more massive and 5,000 times wider – so big that you could pack more than a hundred billion Venuses into its great bulk. So Aldebaran appears fainter than Venus only because of its greater distance – almost four million times farther than the morning star. Look for this mismatched pair beginning a couple of hours before sunrise the next few mornings. Venus will slide to the lower left, and will stand side by side with Aldebaran on Wednesday. They’ll pull apart after that, with Venus dropping a little lower in the sky day by day, and Aldebaran climbing a little higher. Script by Damond Benningfield

Thunderstorms generate what may be nature’s most impressive displays: lightning. And there’s plenty of it; lightning strikes Earth millions of times every day. Although lightning is common, it’s also mysterious. The electric fields inside clouds don’t appear to be strong enough to power lightning. So for the past 90 years, scientists have pondered whether it might have a cosmic origin – cosmic rays – particles that ram into Earth’s atmosphere at almost the speed of light. Many of them come from the Sun. But the most powerful come from exploding stars, the gas around black holes, and other powerful objects in deep space. When a cosmic-ray particle hits an atom or molecule in the upper atmosphere, it creates a shower of other particles. And it’s these particles that might then zip through clouds, creating lightning. A study published earlier this year seems to affirm this idea. Scientists studied a thunderstorm over New Mexico with a sophisticated array of radio antennas. They traced more than 300 strikes from beginning to end, at intervals of less than a thousandth of a second. Among other things, the radio waves revealed that the bolts weren’t moving the way they should if they’d been sparked by the clouds themselves. Instead, the lightning seemed to be triggered by something coming from beyond Earth: cosmic rays. Script by Damond Benningfield

If you throw a rock into a still pond, waves ripple outward. They jiggle the leaves and bugs on the surface, shaking things up a bit. And the same thing happens in the stars. In fact, a giant region of the sky is still feeling some “ripples” today. The Scorpius-Centaurus O-B Association contains many stars of classes O and B – the hottest and brightest stars in the galaxy. It spans hundreds of light-years, and contains thousands of stars. And more stars are being born there today. The association began as a massive cloud of gas and dust. About 20 million years ago, it produced a big “wave” of starbirth. Many of the newborn stars quickly exploded as supernovas. That outburst was the “stone” in the pond. Strong winds and shockwaves from the stars rippled outward. That triggered the birth of more stars in the surrounding cloud. The rate of starbirth peaked about 15 million years ago. But the ripples didn’t stop. They created a smaller outburst about 10 million years ago, and another about five million years ago. Most of the stars in the region are no bigger than the Sun. But a few are big, heavy, and bright – monster stars born from the ripples in a galactic pond. Many of these monsters are in Scorpius, which is low in the south at nightfall, to the right of the Moon. It’s marked by the scorpion’s bright “heart,” the star Antares – the most prominent member of the Scorpius-Centaurus Association. Script by Damond Benningfield

The star that marks the heart of the scorpion is at death’s door. Sometime in the next million years or so, Antares is expected to explode as a supernova. But astronomers don’t know exactly when that’ll happen. There’s no way to see into its core, which is where the fusion reactions that power the star take place. And with current technology, we can’t tell that the end is near by looking at the surface of Antares. The star is many times the mass of the Sun, so when its nuclear engine shuts down, its core will collapse to form a neutron star or black hole. Its outer layers then will blast outward at a good fraction of the speed of light. But the star is so big that the shockwave won’t reach the surface for many hours, so it won’t begin to brighten for hours. The shockwave is powered in part by neutrinos – particles created during the collapse. They almost never interact with other matter, so most of them will zip through the star at almost the speed of light. But there are so many of them that the rare times they do interact will help drive the blast. As the neutrinos race through the galaxy, they’ll reach detectors on Earth hours before the surface of Antares begins to brighten – alerting us to the brilliant demise of a giant star. Antares stands to the upper right of the Moon at nightfall, and leads the Moon down the southwestern sky later on. We’ll have more about the scorpion tomorrow. Script by Damond Benningfield

The Moon will step on the head of the scorpion tonight. It will pass directly in front of one of the stars that outlines the head, blocking it from view – an event called an occultation. Pi Scorpii is actually a system of three stars, about 600 light-years away. The main star in the system is about a dozen times the mass of the Sun, and more than 20,000 times the Sun’s brightness. Because of its great mass, it’s already nearing the end of its life, even though it’s billions of years younger than the Sun. Before long, it will explode as a supernova. The Moon sometimes passes in front of the star because Pi Scorpii lies near the ecliptic – the Sun’s path across the sky. The Moon’s orbit around Earth is tilted a bit, so it roams a few degrees either side of the ecliptic. That allows it to occult quite a few stars that are bright enough to see with the unaided eye. This month alone, in fact, the Moon will stage almost a dozen occultations. But each of them is visible across only a small slice of the globe, so we don’t see all of them from here in the United States. But some of them align just right – allowing us to see the Moon briefly stomp out a star. The occultation of Pi Scorpii will be visible across almost all of the Lower 48 states. The exact time, and how long the star remains blocked, depends on your location. We’ll talk about the Moon and the heart of the scorpion tomorrow. Script by Damond Benningfield

Antimatter may power more than just starships. It might also have helped rev up the BOAT – an exploding star nicknamed “the Brightest Of All Time.” It was seen in October of 2022, in Sagitta, the arrow. Right now, the constellation is in the east at nightfall. The event was a gamma-ray burst – a stellar explosion that aimed “jets” of gamma rays in our direction. It was by far the most powerful cosmic event ever seen. It produced more energy in one second than the Sun will generate in its entire lifetime of more than 10 billion years. It was so powerful, in fact, that it created minor disturbances in Earth’s upper atmosphere – even though it was more than two billion light-years away. The outburst probably happened when a star many times the mass of the Sun died. Its core collapsed to form a black hole, while its outer layers blasted into space as a supernova. As the star died, superheated gas spiraled around the black hole. Magnetic fields directed some of that material into space from the star’s poles. Earth lined up along one of those beams, which is why we saw the outburst of gamma rays. A recent study says that an odd feature recorded during the outburst might have been produced when electrons and their antimatter counterparts rammed together and destroyed each other. That would have added to the energy of the blast – helping make the gamma-ray burst the BOAT – the Brightest of All Time. Script by Damond Benningfield

A giant tarantula creeps through a nearby galaxy. It’s not trying to be stealthy, though – it’s the galaxy’s brightest feature. In fact, it’s the most impressive stellar nursery in the entire Local Group – the cluster of dozens of galaxies that includes the Milky Way. The Tarantula Nebula is in the Large Magellanic Cloud, a companion galaxy to the Milky Way that’s just 160,000 light-years away. Over the last few million years, the nebula has given birth to millions of stars. That’s probably the result of a close encounter with a smaller galaxy. The gravity of the other galaxy caused large clouds of gas and dust to collapse, forming new stars. The Tarantula incorporates several star clusters – groups of stars that all formed at about the same time. The most impressive is R136. It contains a half-million stars, most of which are no more than three million years old. Most of those stars are the mass of the Sun or lighter. But a few are monsters that are many times heavier than the Sun. At least nine of them are more than a hundred times the Sun’s mass. And the biggest of all may be more than two hundred times the Sun’s mass – the heaviest star yet seen in any galaxy, including our own. Within the next few million years, many of these stars are likely to blast themselves to bits as supernovas. In fact, a star on the outskirts of the nebula did just that in 1987 – a brilliant outburst from the tarantula. Script by Damond Benningfield

Fireworks will light up the skies of many cities and towns this week – celebrations of Independence Day. For a real fireworks display, though, you might want to visit one of the Milky Way’s companion galaxies. It’s giving birth to many thousands of new stars, including some of the biggest and brightest yet seen anywhere – a result not of independence, but of a close relationship with another galaxy. The Large Magellanic Cloud is too far south to see from the continental United States. In southern-hemisphere skies, though, it’s quite a sight – a bright cloud that’s several times bigger than the full Moon. The galaxy is much smaller and fainter than the Milky Way. But it’s right next door – just 160,000 light-years away. That’s one of the reasons it looks so bright. Another is that the galaxy contains millions of hot young stars – stars that are thousands of times brighter than the Sun. And it’s giving birth to more. In fact, it contains a stellar nursery that’s far more impressive than anything in the Milky Way. We’ll have more about that tomorrow. The fireworks probably are the result of an interaction with another galaxy, the Small Magellanic Cloud. The smaller galaxy passed close to the bigger one. That encounter squeezed giant clouds of gas and dust. The clouds split into smaller clumps, which gave birth to new stars – creating fireworks in a busy galaxy. Script by Damond Benningfield

The Sun is an impressive star. Its mass ranks in the top 10 percent of all the stars in the galaxy. But the bright star that snuggles up to the Moon the next couple of evenings puts the Sun to shame. It’s bigger and heavier, it has a close companion, and it’s shaped a bit like an egg. And it faces a more dramatic fate. Spica is the brightest star of the constellation Virgo. It consists of two stars – the bright star we see, plus a close companion that we can’t see. We know the companion is there because it reveals its presence to special astronomical instruments. The stars are so close together that their gravitational pull on one another makes both of them look more like eggs than balls. The main star is called Spica A. It’s more than 10 times the mass of the Sun. At that great heft, it gulps its nuclear fuel in a big hurry. That makes the star especially hot and bright – more than 20 thousand times brighter than the Sun. Spica A also is about seven and a half times the Sun’s diameter, and more than 400 times its volume. And its fate is king-sized as well. Within a few million years, it will explode as a supernova – briefly shining as the brightest object in the entire galaxy. Look for Spica to the left or upper left of the Moon this evening. The Moon will slide a bit closer to the star before they set, after midnight. Spica will stand closer to the Moon tomorrow night. Script by Damond Benningfield

When it comes to Earth’s orbit around the Sun, the more things change – well, the more things change. Over the course of a year, our distance from the Sun varies by about three million miles. But that’s changing. And we’re farthest from the Sun in early July – but that’s changing, too. The farthest point from the Sun is known as aphelion – from Greek words that mean “far from the Sun.” And we’ll reach that point on Thursday. Earth will receive about seven percent less sunlight than it does when we’re closest to the Sun, in early January. Earth’s orbit around the Sun is elliptical – like a slightly flattened circle. But the exact shape changes over a period of about a hundred thousand years. Right now, the orbit is getting a little more circular, so there’ll be a smaller change in the distance to the Sun. After that, it’ll get a lot more stretched out. That will cause much bigger changes in Earth’s climate between the closest and farthest points. The timing of those points also changes. About 800 years ago, aphelion happened around the time of the summer solstice in the northern hemisphere. Now, it’s shifted a couple of weeks later. And the shift is continuing. So, about 4400 years from now, aphelion will happen at the fall equinox, in September. It’ll return to its current spot on the calendar more than 20,000 years from now. Tomorrow: A bright star that looks like an egg. Script by Damond Benningfield

Lots of star clusters adorn the evening skies of summer. That’s because the glowing path of the Milky Way climbs high into the sky. It’s the combined glow of millions of stars that outline the disk of the Milky Way Galaxy. So not only does it contain lots of individual stars, it hosts many star clusters as well. But a few clusters are far from the path of the Milky Way. One example is Messier 5. It’s in Serpens Caput – the head of the serpent – a region with not much around it. M5 is a globular cluster – a big ball packed with several hundred thousand stars. Such clusters are scattered all across the sky. Some appear in the disk, but they’re not part of the disk – they loop high above and below it. Globular clusters are the oldest members of the galaxy. And M5 is one of the oldest – 12 billion years or older. That means its original stars were born when the universe was only about one-tenth of its present age. Any stars that were more massive than the Sun have burned out. So the remaining original stars are smaller and fainter than the Sun. There’s evidence that a second wave of starbirth rippled through M5 well after the cluster was formed. Some of these stars can still rival the Sun – the “youngsters” of an ancient star cluster. Messier 5 is high in the south at nightfall. Through binoculars, it looks like a fuzzy star. A small telescope reveals some of the cluster’s individual stars. Script by Damond Benningfield

Mars and the Moon stage a spectacular encounter this evening. The Moon will slide just a fraction of a degree from the planet, which looks like a bright star. Something we’ve learned about both of these worlds is that they have a lot of frozen water. On the Moon, it’s mixed in with the dirt and pebbles, or buried in craters that never see the Sun. On Mars, it’s also mixed in at the surface, but it’s also found in the polar ice caps, in layers of frost, and elsewhere. On Mars, there’s even evidence of liquid water far below the surface. A study last year said there could be a lot of water buried in spaces in the rocks about 10 miles down – enough water to cover the surface of Mars in an ocean about a mile deep. And earlier this year, scientists in Japan reported more evidence of that water. They analyzed the observations of the InSight lander, which operated for four years. The craft listened for “marsquakes.” Sound waves from the quakes traveled through the planet. The new study looked at how different types of waves rippled through the interior. Each type of wave travels differently as it passes through different materials – rock versus water, for example. So comparing the waves revealed the likely presence of water miles below the surface. On Earth, where there’s water, there’s life. So an ocean’s-worth of water could provide a home for life on the Red Planet. Script by Damond Benningfield

The crescent Moon and two bright pinpoints stairstep up the western sky this evening. Regulus, the star that represents the heart of the lion, is to the upper left of the Moon. And the planet Mars is about the same distance to the upper left of Regulus. The trio sets in late evening. The largest feature on the Moon has never been seen directly by human eyes – only by robots. That’s because it’s on the Moon’s far side – the hemisphere that always faces away from us. Only a sliver of its edge can be seen from Earth. And Apollo astronauts saw only a sliver of the opposite edge. South Pole-Aitken Basin is about 1600 miles wide – one of the largest impact features anywhere in the solar system. It probably formed when a giant asteroid slammed into the Moon soon after the Moon was born. A Chinese lander, Chang’e 6, touched down in the basin last June. A few weeks later, it brought about four pounds of rocks and dust to Earth. Analysis of some of the samples confirmed that the basin was gouged four and a quarter billion years ago. But the dark volcanic rock that coats much of the basin formed just 2.8 billion years ago, when an ocean of magma cooled and crystallized. Samples from the near side of the Moon indicate that it was coated with magma at the same time. So the entire lunar surface was covered by an ocean of molten rock – the side we can see, and the side we can’t. Script by Damond Benningfield

Two decades before astronauts walked on the Moon, American movie-goers got a good preview of what the trip might look like. “Destination Moon” was the first big space movie. And it was the first to accurately explain the science and engineering of a trip to the Moon. Co-written by science-fiction author Robert Heinlein, the movie premiered 75 years ago today. In the story, millionaire businessmen decide to finance a lunar voyage. They build a nuclear-powered rocket in the desert, then send it on its way. Problems ensue, but the crew lands on the Moon and makes it back home safely. The backers are convinced in part by a short cartoon that accurately explained how rockets work. In fact, the cartoon was so good that NASA later used a revised version to explain rockets to the public. Destination Moon also showed the effects of acceleration and zero-gravity. During a spacewalk, one of the crew maneuvered using a tank of oxygen; the first real American spacewalker used a similar technique. And on the Moon, the crew loped along just like the Apollo astronauts. The film didn’t get everything right. The landscape – painted by space artist Chesley Bonestell – was too sharp and craggy. And the art director added cracks to the surface like those in a dry riverbed to add a feeling of depth. Still, Destination Moon remains one of the most accurate movies about spaceflight – a fantastic trip to the Moon long before the real thing. Script by Damond Benningfield

Early in its history, the inner solar system was chaotic. Violent collisions might have destroyed many small worlds, while perhaps creating others – including the Moon. It probably formed when a planet as big as Mars rammed into Earth, blasting out debris that came together to make the Moon. A recent study says that a meteorite discovered a few years ago might be a remnant of one of the demolished worlds. NWA 15915 was discovered in Algeria. Scientists analyzed the composition, structure, and magnetic properties of the six-pound meteorite. They concluded that it’s a rare type of meteorite – it doesn’t come from any known asteroid, planet, or moon. But it does have some similarities to Mercury, the smallest planet and the one closest to the Sun. The study suggests that NWA 15915 might have come from a Mercury-like planet born in the same region of the solar system. The planet was demolished long ago by a giant impact. But a few fragments remain. The findings are preliminary. So it’ll take more work to confirm that a piece of a dead planet fell atop the desert sands of northwestern Africa. Mercury itself is near the Moon this evening. It looks like a fairly bright star to the left of the Moon. They’re quite low in the sky as twilight fades, so you need a clear horizon to spot them. Script by Damond Benningfield

It would be fascinating to get close to Cygnus X-3. Unfortunately, it also would be deadly. The system is bathed in X-rays and ultraviolet radiation. It features powerful “jets” that blast into space like energy cannons. And it probably has a black hole – a one-way trip to oblivion. Cygnus X-3 is in the swan, which swoops across the eastern sky on these early summer evenings. The system itself is too faint to see. In fact, we can’t see its visible light even with the largest telescopes because it’s hidden behind thick clouds of dust. But we can see it in other wavelengths, including X-rays, gamma rays, and radio waves. Those forms of energy have allowed astronomers to piece together the system’s likely story. Cygnus X-3 probably consists of a black hole plus a brilliant companion. The companion probably is a dozen or more times the Sun’s mass, and a couple of hundred thousand times its brightness. The bright star is blowing huge amounts of gas into space. The black hole grabs some of the gas, which forms a spinning disk around the black hole. Some of the gas is funneled into high-speed jets that fire into space. One of those jets is aimed almost directly at Earth. The brilliant companion star is likely to explode in the next million years or so, with its core collapsing to form another black hole. But the blast might rip the system apart – perhaps causing Cygnus X-3 to fade away. Script by Damond Benningfield

425 years ago, a “new” star flared to life near the neck of Cygnus, the swan. The star slowly faded, then flared twice more during the 17th century. It’s remained visible ever since. And someday soon, it’ll flare up again – for the last time: It’ll explode as a supernova. P Cygni is more than 5,000 light-years away, so it must be extremely bright for us to see it at all. And in fact, it’s one of the brightest stars in the entire galaxy – 600 thousand times brighter than the Sun. P Cygni is so brilliant because it’s 35 to 40 times the mass of the Sun. Such a monster burns through the nuclear fuel in its core in a hurry. So even though P Cygni is only a few million years old – compared to four and a half billion years for the Sun – it’s nearing its end. The earlier outbursts might have erupted because the star’s interior is unstable. It gets so hot that the star blasts some of the gas at its surface into space. There’s evidence that similar outbursts took place thousands of years earlier. P Cygni is likely to explode within a couple of million years. Its core might collapse to form a super-dense neutron star – or even a black hole. Under dark skies, P Cygni is visible to the eye alone. At nightfall, it’s in the east-northeast, close to the right of Sadr, the bright star that connects the swan’s body to its wings. More about the swan tomorrow. Script by Damond Benningfield

Cygnus, the swan, soars gracefully through summer nights. Its brightest star, Deneb, is in the northeast at nightfall. It marks the swan’s tail. The swan’s body stretches to the right, parallel to the horizon. The wings extend above and below, connected to the body by the star Sadr. Cygnus contains many star clusters. The list includes several that stretch from Sadr to the south, roughly along the swan’s neck. The clusters contain a few dozen to a few hundred stars. All of them are young – no more than about 10 million years old. And many of them are especially hot, bright, and massive. The clusters are indirectly related. They belong to much larger collections of young stars, plus the raw materials for making more stars. A “wave” passed through that region of the galaxy, squeezing gigantic clouds of gas and dust. Clumps of material within the clouds collapsed, forming stars. Over the next few million years, the most massive stars will explode as supernovas. Shockwaves from the blasts may compress more pockets of gas and dust, creating more stars. But the clusters themselves won’t survive much longer – at least on the galactic timescale. They’ll be pulled apart by the gravity of the surrounding stars and clouds, so their stars will go their separate ways. The clusters are easy targets for good binoculars. One is just a whisker from Sadr. Several others trail off to the right – sparkly decorations for the swan. Script by Damond Benningfield

The Royal Observatory at Greenwich has been one of the most important skywatching sites in history – not so much for what it told us about the stars, but for its role right here on Earth. Its location marked the starting point for measuring longitude – the position east and west on the globe. It also marked the time standard for the entire world: Greenwich Mean Time. The observatory was established on today’s date in 1675, by King Charles II. It was built on a hill near London, overlooking the Thames. Greenwich was created to provide highly accurate maps of the stars, and to measure the motions of the Sun, Moon, and planets. The work was designed to help sailors determine their longitude. Establishing longitude at sea was extremely difficult – and dangerous; many ships crashed because their navigators didn’t know where they were. The observations also played a key scientific role: they helped confirm that the motions of the Sun, Moon, and planets were governed by Isaac Newton’s laws of gravity. In 1833, the observatory began a “time service.” It dropped a ball from a tall pole at precisely 1 p.m. That allowed mariners to set their clocks before they sailed. Greenwich later transmitted the time to the whole country by telegraph, then radio. The observatory was moved in the 20th century, and closed in 1998. Today, the Greenwich site is a museum – preserving an important part of world history. Script by Damond Benningfield

The only astronomical object most of us notice in the daytime sky is our star, the Sun. Its light makes the sky bright, which overpowers the other stars and almost everything else. But there are a couple of exceptions: the Moon and the planet Venus. During its 29-and-a-half-day cycle of phases, the Moon spends half of its time in the daytime sky – the hours between sunrise and sunset. But it’s so pale compared to the Sun that it can be hard to notice. That’s especially true when the Moon is in its crescent phase, as it is now. At dawn tomorrow, the Sun will light up only about one-eighth of the lunar hemisphere that faces our way. So the Sun will look millions of times brighter than the Moon. As twilight begins, the Moon will continue to dominate the sky. But as twilight gets brighter, the Moon will appear to fade. It’s still just as bright, but against the daytime sky it’s hard to see. But you can still spot it, leading the Sun across the sky. At dawn, Venus stands to the lower right of the Moon. It’s the brilliant “morning star.” Until sunrise, only the Moon outshines it. Venus also fades into the blue of the daytime sky. But it is visible to the unaided eye. It leads the Moon up the sky in the morning, and down the sky in the afternoon. It’s hard to find, but once you see it, you’ll wonder why you never noticed it before – a bright planet shining through the bright blue sky. Script by Damond Benningfield

The Sun is at a standstill. Oh, it’s still orbiting the center of the galaxy at an impressive clip – about half a million miles per hour. And it’s still moving across the sky as Earth turns on its axis. But the points along the horizon at which the Sun rises and sets aren’t changing. That’s because today is the summer solstice. It’s a point in Earth’s orbit that marks the beginning of summer in the northern hemisphere and winter in the southern hemisphere. We have seasons because Earth is tilted on its axis. At the June solstice, the north pole tilts toward the Sun, bringing more sunlight to the northern hemisphere. Six months later, the south pole tilts toward the Sun, giving the northern half of the globe shorter days and longer nights. Between the solstices, the Sun moves north and south in the sky. So its rising and setting points move north and south as well. At some times of year, if you have a good way to mark these points, you can see the difference from day to day. But the Sun appears to “stand still” along the horizon for a few days on either side of the solstice. In fact, the word solstice means “Sun stands still.” At the June solstice, the Sun is farthest north for the year, so it rises and sets to the north of due west. Just how far north depends on your latitude. Incidentally, the summer solstice is also the longest day of the year, so there’s plenty of sunlight as we head into summer. Script by Damond Benningfield

The number of confirmed planets in other star systems has reached about 6,000. But few of those planets are likely homes for life. Most are too hot, too cold, too “gassy,” or they’re zapped by too much radiation by their star. A few planets are in the “well, maybe” category. They might be suitable for life, but the conditions aren’t perfect. An example is a planet in the star system 82 Eridani. The system is about 20 light-years from Earth, and its star is similar to the Sun. Astronomers have confirmed three planets in the system, with hints of more. Two of the planets are quite close to the star, so they’re too hot for life like that on Earth. But the third planet is more intriguing. It’s about six times the mass of Earth, so it could be dense and rocky. Its average distance from the star is about a third farther than Earth’s distance from the Sun. At that range, the planet spends most of its time in the star’s habitable zone – the region where conditions are most comfortable for life. But the planet’s orbit is so lopsided that the distance varies by more than a hundred million miles. So as the planet moves around 82 Eridani, surface temperatures range from hot enough to boil water to cold enough to freeze the entire surface. That makes it unlikely that anything lives on the planet. It is possible that life could exist below the surface – avoiding the extremes on this “yo-yoing” planet. Script by Damond Benningfield

Astronomers have been searching for planets around one of our closest neighbor stars for decades. And they’ve reported the discovery of several. But the reports have come to naught – until now. Earlier this year, a team confirmed the presence of four planets – all of them smaller than Earth. Barnard’s Star is six light-years away. Only the three stars of the Alpha Centauri system are closer. The star is much smaller and less massive than the Sun, and less than one percent as bright. In fact, it’s so faint that it wasn’t discovered until a little more than a century ago. Barnard’s Star is ancient – probably twice the age of the Sun or older. So if it has planets, there’s been plenty of time for life to take hold. That’s made finding planets a high priority. Last year, a team of astronomers confirmed one planet, and said there might be three more. All of those were confirmed in March. None of the planets is more than a third the mass of Earth. And they’re so close in that they orbit the star in a week or less. So even though Barnard’s Star is faint, the planets are all too hot to provide comfortable conditions for life. Barnard’s Star is in Ophiuchus, the serpent-bearer. The constellation stretches across the east and southeast in early evening, and stands high in the south later on. But Barnard’s Star is too faint to see without a telescope. We’ll have more about exoplanets tomorrow. Script by Damond Benningfield

If you stare at one of the giant planets of the outer solar system long enough, with a big enough telescope, you’re likely to find some moons. That was certainly the case a couple of years ago for Saturn. A research team scanned the space near Saturn with a large telescope in Hawaii. And earlier this year, the team reported its results: a haul of 128 previously unseen moons. That brought the planet’s total to 274. That’s three times the number of moons for second-place Jupiter – at least for now. The newly found moons are small and faint – no more than a few miles in diameter. They follow odd orbits, including some that orbit backwards – in the opposite direction from Saturn’s rotation. Some of the moons may be chunks of space rock that were captured by the giant planet’s gravity. Others may be the remains of larger moons that were blasted apart by collisions. About a third of the moons may be the remnants of a single impact. They form a group named Mundilfari for a Norse god related to Saturn. It’s possible the impact took place within the past hundred million years – adding lots of little moons to Saturn’s family. Look for Saturn near our own moon the next couple of mornings. The planet looks like a bright star. It’ll stand to the lower left of the Moon at dawn tomorrow, and closer to the right of the Moon on Thursday. Tomorrow: a passel of planets for a nearby star. Script by Damond Benningfield

If you sit on a big beachball, it gets mashed down. That makes it a little wider through the middle, and a little narrower from top to bottom. And that makes it look a lot like Alderamin, the brightest star of the constellation Cepheus the king. The star is about a third wider through the equator than through the poles. That’s not because some cosmic giant is sitting on it. Instead, it’s because the star spins like crazy. Alderamin is about 50 light-years away, so it’s a fairly close neighbor. It’s nearing the end of the prime phase of life, even though it’s billions of years younger than the Sun. That’s because it’s twice as massive as the Sun. Heavier stars “burn” through their nuclear fuel much faster than lighter stars. What really stands out about Alderamin, though, is its shape. The star’s equator rotates once every 12 hours, versus almost four weeks for the Sun. That forces gas outward around its middle, making the star look a bit more like a fat lozenge than a ball. As Alderamin continues to age, though, it will puff up to many times its current diameter. That will slow down its high-speed rotation, giving Alderamin a “rounder” appearance. Cepheus is in the north and northeast at nightfall. Under fairly dark skies it’s easy to make out. It looks like a child’s drawing of a house. The peak of the roof is on the left during the evening, with Alderamin marking the top right corner of the sideways house. Script by Damond Benningfield

Capricornus may be the most inventive constellation of the zodiac. For one thing, all of its stars are faint, so it takes some work to see any kind of pattern there. And for another, it represents the oddest creature in the heavens: a sea-goat – the front half of a goat plus the tail of a fish. It’s easy to find the sea-goat’s location early tomorrow, because the Moon passes quite close to its brightest star. Unfortunately, the Moon will overpower most of the nearby stars, so you might want binoculars to help you see them. The sea-goat’s leading light is known as Delta Capricorni or Deneb Algedi – the tail of the goat. It’s about 39 light-years away. It’s actually two stars locked in orbit around each other. The main star is twice the size and mass of the Sun, and about eight times the Sun’s brightness. The other star is smaller and fainter than the Sun. Twice a day, Delta Cap fades a bit. That’s because its stars orbit each other once per day. And they’re aligned in such a way that they eclipse one other during each orbit. The system dims a bit more when the faint star passes in front of the bright one, and a bit less when it’s the other way around. The stars of Capricornus form a wide triangle. Delta Cap is at the left point of the triangle. It climbs into good view by about 1 a.m. less than a degree from the bright Moon. Script by Damond Benningfield

A perfect spiral galaxy would include a bright, round “bulge” of stars in the middle; glittering spiral arms wrapping around it; dark lanes of dust lacing through the arms; and bright star clusters sprinkled about like lights on a Christmas wreath. In other words, it would look just like Messier 81, one of the best examples of a “grand design” spiral galaxy. It’s about 12 million light-years away, and appears close to the bowl of the Big Dipper. It’s a bit smaller and less massive than our own home galaxy, the Milky Way. M81’s “bulge,” though, is much larger and brighter than the one in the center of the Milky Way. And the black hole in the galaxy’s heart is almost 20 times as massive as the Milky Way’s. The spiral arms are outlined by the galaxy’s youngest, brightest stars. Over the past 600 million years or so, a major bout of starbirth has brightened the arms. That outburst is the result of gravitational interactions between M81 and two companion galaxies. The encounters compress big clouds of gas and dust. The clouds break into clumps, which then collapse to form stars – stars that make Messier 81 one of the most beautiful galaxies of all. Under clear, dark skies, you can spot M81 with binoculars. Find the Big Dipper, which is high in the north at nightfall. M81 hangs below the bowl at that hour. It looks like an oval smudge of light that’s almost as wide as the Moon. Script by Damond Benningfield

The stars look like they’re stuck in position – like fairy lights thumbtacked to a giant black canvas overhead. And over the course of a human lifetime – or many lifetimes – that’s true – there’s no way to see any motion without the help of sensitive instruments. But that’s only because the stars are so far away. Every one of those little lights is moving – fast. They’re all orbiting the center of the Milky Way Galaxy, for example. And they’re moving either toward or away from Earth. So over millions of years, the configuration of the stars changes – constellations come and go. And the pattern of brightness changes as well – some stars fade, others grow brighter. An example is Eltanin, the brightest star of Draco, the dragon. In fact, its name means “the great serpent.” It represents one of the dragon’s glowing eyes. Today, Eltanin is a bit more than 150 light-years away. But it’s moving more or less toward us at more than 60,000 miles per hour. On the scale of the galaxy, that’s tiny – but it adds up. In about one and a half million years, it’ll be just 28 light-years away. If the star doesn’t change much over that period, it could be the brightest star in Earth’s night sky. And it could maintain that rating for hundreds of thousands of years. Look for Eltanin high in the northeast at nightfall. It’s to the upper left of Vega, one of the brighter stars in the night sky – for now. Script by Damond Benningfield

Two fairly bright lights are headed for an especially close meet-up: the planet Mars and the star Regulus, the heart of the lion. They’re a few degrees apart tonight, but they’ll draw even closer over the coming evenings. Right now, Mars and Regulus are almost the same brightness. One way to tell them apart is their color – Mars looks pale orange, while Regulus is white with a hint of blue. Binoculars accentuate the colors. Another way to tell them apart is to look for them to twinkle. Regulus does, but Mars doesn’t. That’s because Mars is a bigger target in our sky. Regulus is thousands of times the size of Mars. But it’s so far away that we see it as nothing more than a pinpoint. That tiny beam of light is bent and twisted as it passes through the atmosphere. That causes the star to “twinkle.” It twinkles more when the air is more unsettled. Mars, on the other hand, is close enough that it appears as a tiny disk, made up of many pinpoints. Each one twinkles, but they even out. So Mars appears to hold steady as it shines through even the most un-steady skies. Look for Mars and Regulus about a third of the way up the western sky at nightfall. Regulus perches to the left or upper left of Mars. They’ll pass closest to one another on Monday and Tuesday. After that, they’ll move apart. At the same time, Mars will fade. A couple of weeks from now, Regulus will clearly outshine the Red Planet. Script by Damond Benningfield

Anchorage, Alaska, isn’t quite the “land of the midnight Sun.” Tonight, there are about five hours between sunset and sunrise. But it is a land of midnight sunlight, because twilight never completely fades. Twilight is the transition between day and night. Earth’s atmosphere scatters sunlight from the dayside to the fringes of the nightside. But when, exactly, does twilight end? When is the sky really dark? As you might expect, astronomers have their own definition. Astronomical twilight begins or ends when the Sun is 18 degrees below the horizon – about twice the width of your fist held at arm’s length. That’s when the sky’s as dark as it’s going to get. Because of the Sun’s motion, astronomical twilight lasts a minimum of about an hour and 10 minutes. But because the Sun usually rises and sets at an angle, twilight can last a good deal longer. During much of June and July, when the days are longest, twilight for much of the northern hemisphere lasts all night. The Sun never drops far below the horizon, so even though it’s out of sight, its light never disappears. So the people of Anchorage need some good blackout curtains to get a dark night’s sleep. If you want a few hours of darkness, head south – someplace like Miami Beach. It gets a full seven hours between evening and morning twilight – hours that might be illuminated by the neon lights of South Beach, but not by the Sun. Script by Damond Benningfield

Cold hands, warm heart. Still waters run deep. Feed a cold, starve a fever. The list of pithy old sayings goes on and on. But here’s a new one for you: long Sun, short Moon. It means that the full Moon does the opposite of what the Sun does. So when the Sun is in the sky for a long time, the full Moon makes itself scarce. And that’s the case tonight. The full Moon of June has many names, including Flower, Strawberry, and Honey Moon. But it’s also known as the Short-Night Moon. That’s because it’s in view for less time than any other full Moon of the year. From the northern hemisphere, the Sun passes highest across the sky at this time of year, and remains in view longest. But because of the trail they follow, the Sun and the full Moon are like opposite ends of a seesaw. When one is up, the other is down. So right now, the full Moon passes low across the sky. And it rises around sunset and sets around sunrise. The difference is greater as you go farther north. From Miami, the Sun will be above the horizon for almost 14 hours today, with the Moon popping into view for less than 10 and a half hours. From Duluth, Minnesota, it’s almost 16 hours versus less than eight hours. And from Anchorage, the Sun graces the sky for 19 hours, with the Moon showing up for a stingy hour and a half – an especially short appearance for the Short-Night Moon. More about night and day tomorrow. Script by Damond Benningfield

On average, Antares is the fifteenth-brightest star in the night sky. It looks like an orange-red gem at the heart of the scorpion. Tonight, though, it looks a little feeble. It hasn’t gotten any fainter. Instead, it stands especially close to the almost-full Moon. It looks a little washed out in the powerful moonlight. Antares really is one of the more impressive stars in the galaxy. It’s probably 12 to 15 times the Sun’s mass, hundreds of times the Sun’s diameter, and tens of thousands of times its brightness. Ere long – at least on the astronomical timescale – Antares will get even more impressive – but only for a while. Sometime in the next million years or so, it’s expected to blast itself apart in a titanic explosion – a supernova. For a few months, it’ll shine brighter than the combined glow of billions of normal stars. As it fades, its demolished outer layers will form a nebula – a colorful cloud of gas and dust, energized by the blast and by the decay of radioactive elements. Over thousands of years, the nebula will expand and fade. That will leave only the star’s dead core – a tiny, super-dense corpse known as a neutron star – the almost-invisible remnant of the mighty heart of the scorpion. Antares stands close to the Moon at nightfall, and the Moon will move closer to it during the night – washing out this brilliant star. We’ll have more about the Moon tomorrow. Script by Damond Benningfield

The rings of Saturn are among the most beautiful features in the solar system. They’re wide enough to span the distance between Earth and the Moon. And they’re made of bits of ice and dust – like tiny “moonlets” orbiting the giant planet. The first person to propose that idea was Giovanni Cassini, who was born 400 years ago today. He worked in several fields, from astrology to engineering. But Cassini’s greatest love was astronomy. He became director of the Paris Observatory, and studied the Moon and planets – especially Saturn. He discovered four of its moons, plus a dark “gap” between its two most prominent rings. That gap was named the Cassini Division in his honor. Although it looks empty, the gap contains a smattering of dark particles. It probably was mostly cleared out by a small moon that orbits inside the gap. Its gravity pushes ring particles away. A study a few years ago said the gap could have started much smaller than it is today. Over the past few million years, the moon moved closer to Saturn, clearing a wider region. But now, it’s moving away from Saturn. So the Cassini Division could close up – in about 40 million years. Saturn is in the southeast at dawn, and looks like a bright star. We’re viewing the rings almost edge-on, so there’s not much to see even through large telescopes. But the view will improve over the coming months – revealing both the rings and the dark divide between them. Script by Damond Benningfield

The world has known many great astronomers, but only a few great astronomy dynasties. One of those celebrates an anniversary tomorrow – the birth of its patriarch 400 years ago. Giovanni Cassini was born in a small Italian village just across the border from Nice, France. Cassini the first, as he’s often called, was the first of four generations of Cassini astronomers. And he definitely was the most productive. He’s best known for his discovery of a gap in the rings of Saturn. It’s named the Cassini Division in his honor. Later, Cassini and his son Jacques theorized that the rings were made of “swarms of tiny satellites” moving at different speeds. They understood the truth many years before it was actually confirmed. More about Cassini and Saturn’s rings tomorrow. Cassini made many other contributions to astronomy. He was among the first to realize that light travels at a limited speed, although he didn’t believe the speed could be calculated. And he developed a law to explain why we always see the same side of the Moon: The Moon takes the same amount of time to orbit Earth as it does to complete one turn on its axis. For most of his career, Cassini was director of Paris Observatory. His descendants kept the job in the family for more than 120 years. Cassini the fourth ended the streak in 1793 – when he left the observatory to write the “stellar” history of this astronomical dynasty. Script by Laura Tuma

There was a lot of talk earlier this year about an asteroid with the highest odds of hitting Earth ever calculated. The chances of an impact by asteroid 2024 YR4 in December of 2032 peaked at about three percent. The asteroid is big enough to cause major damage if it hit. As astronomers tracked it a little longer, though, they realized that’s not going to happen – the asteroid will miss by at least 60,000 miles. Such close calls aren’t rare. Hundreds of asteroids pass within a few million miles of Earth every year. This weekend, in fact, asteroid 2014 LL26 will miss us by just two million miles. Its orbit overlaps Earth’s orbit, so it passes close fairly often. And it could hit our planet at some point in the future – though not anytime soon. Astronomers have discovered more than 27,000 potentially hazardous asteroids. And they discover more all the time. The one that caused the kerfuffle earlier this year, in fact, was just discovered in December. Several automated searches scan the sky every night. Those efforts yield thousands of asteroids every month. But it takes observations over a period of days or weeks to give us a good measurement of an asteroid’s orbit. Most of the new discoveries are in the asteroid belt, between the orbits of Mars and Jupiter. But some are close enough to keep an eye on – potential hazards to life on Earth. Script by Damond Benningfield

The Pilbara region of Western Australia is big, dry, and wide open. And it may contain the oldest cosmic “scar” on Earth: an impact crater gouged three and a half billion years ago. Scientists discovered evidence of the crater during a brief expedition in 2021. They found some rock formations called shatter cones. Some of the cones are as tall as a house. The only known way to make them is in giant collisions with space rocks. Follow-up work last year revealed many more of these formations. The cones were found in a rock layer that’s miles wide, but only a few dozen feet thick. The layer also contains tiny “beads” that formed when molten rock was blasted high into the sky. The flight through the air sculpted droplets of the molten rock into balls. Geologists found that the layer formed three and a half billion years ago, so that’s when the impact must have taken place – more than a billion years earlier than the previous record holder. The asteroid could have been miles wide, and blasted a crater more than 60 miles across. The effects of the collision would have been felt around the world. In fact, researchers say the impact could have helped shape the world. Major asteroid impacts could have traveled deep, churning things up far below the surface. That could have created the “seeds” that gave birth to the continents when Earth was young. We’ll talk about potential future impacts tomorrow. Script by Damond Benningfield

You can’t tell just by looking, but the universe undergoes constant change. Stars explode. Quasars flare up. Asteroids zip past Earth. And soon, astronomers will be able to generate super-high-definition movies of those changes almost every night of the year. That’s because a new telescope dedicated to “time-domain” astronomy is about ready to take its first looks at the heavens. The telescope is the centerpiece of the Vera Rubin Observatory. It’s named for an astronomer who provided strong evidence for the existence of dark matter. It’s atop an 8700-foot mountain in Chile. The telescope’s main mirror, which gathers and focuses starlight, is 8.4 meters across – almost 28 feet. It has a wide field of view, allowing it to photograph the entire southern sky every few nights. It’ll record its observations on the largest digital camera ever built – 3200 megapixels. Astronomers will use those observations to learn more about dark energy and dark matter, and to map the Milky Way Galaxy. And they’ll watch for things that change. They’ll discover asteroids and comets – both close to Earth and deep in the outer solar system. They’ll see novas, supernovas, and other brilliant flare-ups. And the observatory will send out immediate notices of each new outburst, allowing other astronomers to make detailed follow-up observations – learning much more about our constantly changing universe. Script by Damond Benningfield

Before astronauts could land and walk on the Moon, NASA had to be sure they could do three things: live in space for days at a time, catch and link up with other spacecraft, and work outside their ship. And it took stabs at two of those goals 60 years ago today, with a mission called Gemini 4.   [AUDIO: 3, 2, 1, Ignition … Liftoff …] Astronauts James McDivitt and Ed White were scheduled to spend four days in space. That was longer than the first seven American missions combined. And White would make the first American spacewalk. He’d float outside the cabin for a few minutes, using a small “gun” of compressed air to move around. And three and a half hours after launch, it was time to get started: CAPCOM: Gemini 4, Hawaii capcom. We just had word from Houston, we’re ready to have you get out   whenever you’re ready. Okay, my feet are out. … Okay, I’m out. The spacewalk went well – very well. [WHITE: I feel like a million dollars!] In fact, it went so well that White didn’t want it to end. HOUSTON: The flight director says get back in!      McDIVITT: This is Jim, you got any message for us?      CAPCOM: Gemini 4, get back in!      McDIVITT: Okay… Actually working during a spacewalk turned out to be a lot harder than White had made it look. It took several more missions to work out the kinks. But the success of Gemini 4 helped make it possible for astronauts to walk on the Moon just four years later. Script by Damond Benningfield

If you step outside at dawn on June third of 2033, you’ll see the planet Venus standing due east – the brilliant “morning star.” But if you don’t want to wait that long to experience that beautiful view, then take a look at dawn tomorrow – Venus will be standing in the same spot in the sky. Not only that, it stands at that spot in the sky every eight years. In fact, anytime you see Venus – whether as the morning star or evening star – you can find it at that same spot eight years later. That’s because there’s a near-“resonance” in the orbital cycles of Earth and Venus. Venus completes 13 orbits around the Sun for every eight orbits that Earth makes. The ratio isn’t exact, but it’s quite close. Thanks to that, Venus follows five repeating cycles across our sky. It’s like the planet is a toy train on a looping, winding track. It hits every point along the track with every cycle. If you plot that motion from the perspective of Earth, it traces out a flowing pattern like five rose petals. The clockwork precision makes it easy to predict the entire sequence of Venus’s appearances. We know that it always remains in view in the morning sky for about 263 days, disappears for about 50 days, then moves into the evening sky. So if you miss the view of Venus tomorrow, or the next day, or the day after that, just mark it in your calendar – and look for it in the same location eight years later. Script by Damond Benningfield

The Moon has regular dates with the stars. It returns to the same position relative to the stars every 27 days and eight hours. As an example, the Moon cozied up to Regulus, the bright heart of the lion, on May 5th, and it does so again this evening – 27 days, eight hours later. This encounter is especially close as seen from the United States – the Moon and Regulus will appear to almost touch each other. That time span is known as the lunar sidereal period – “sidereal” meaning “related to the stars.” The planets have their own sidereal periods. Mars, for example, returns to the same point relative to the stars every 22 and a half months. Tonight, Mars is well to the lower right of Regulus, and looks like an orange star. It’ll return to almost the same position in April of 2027. The match won’t be exact because our viewing angle to the Red Planet changes a bit from year to year. The sidereal period is different from the period relative to the Sun – a difference caused by Earth’s own orbital motion. For the Moon, that period lasts 29 and a half days – the length of a cycle of phases. And for Mars, the Sun-related period is almost 26 months. That’s how long it takes Mars to return to the same angle from the Sun – part of the precise but sometimes confusing motions in the night sky. More about the motions of the planets tomorrow. Script by Damond Benningfield

To the more poetic among us, summer is a time of soft breezes, warm nights, and fireflies: The livin’ is easy, the breeze makes us feel fine, the warm Sun shines kindly upon us. But there’s less poetry in the summers on Mars – especially in the northern hemisphere, where summer began on Thursday. It stays cold, and the only fireflies are occasional meteors blazing through the night. Like the seasons on Earth, those on Mars are caused by the planet’s tilt on its axis. Northern summer begins when the north pole dips most directly toward the Sun. But Mars’s orbit is much more lopsided than Earth’s, so there’s a much greater change in the planet’s distance from the Sun. Mars is farthest from the Sun during northern summer. So the summer stays fairly cool. Summers and winters tend to be quiet times in the planet’s thin atmosphere. Big dust storms fire up in spring and fall, sometimes covering the whole planet. But they settle down by the start of summer. Mars does see more “dust devils” during summer – whirlwinds that can tower miles high. Northern summer will last for 178 Mars days – not giving way until the start of autumn exactly six months from now. Mars is close to the upper left of the Moon at nightfall, and looks like a fairly bright orange star. The true star Regulus is farther along that line. More about this lineup tomorrow. Script by Damond Benningfield

The United States plans to send astronauts to the Moon later in this decade, aiming toward a permanent lunar base. But experience shows that plans come and go. In fact, if all the plans for lunar exploration had actually come about, we’d be skittering all across the Moon today. In 1958, for example, the Air Force developed Project LUMAN, a comprehensive plan for human spaceflight. It would culminate with a single astronaut landing on the Moon. Later, the service developed another plan – LUMEX. It called for three astronauts to travel to the Moon using a giant new booster and a streamlined spaceship. The Army developed its own plan, involving a space station and other steps. All of those plans died – in part because human spaceflight was turned over to a new civilian agency: NASA. And NASA had its own false steps. It studied using its two-man Gemini spacecraft for lunar missions before settling on Apollo. And even then, some of its plans were scuttled; the final three Apollo missions were scrapped, in 1970. President George W. Bush proposed lunar missions as part of the Constellation program. It was nixed by President Obama. But some of its hardware has been kept for Artemis – which plans to send astronauts to the Moon in the next few years. Look for the Moon in the west at nightfall. The twin stars of Gemini stand to its lower right, with Mars to its upper left – another planned destination for human explorers. Script by Damond Benningfield

Globular clusters are the oldest members of the galaxy. They’re tight balls of hundreds of thousands of stars, most of which were born when the universe was no more than a couple of billion years old. Their most-massive stars have long since died. And most of the stars that remain are cool and faint. So a globular tends to be fairly quiet and calm. But that doesn’t mean that things don’t change. Consider Messier 13. It’s in Hercules, which is high in the east at nightfall. Under dark skies, the cluster is just visible to the unaided eye, looking like a faint, fuzzy star. The cluster is about 25,000 light-years away, and it contains up to half a million stars. But the stars at the edge of the cluster aren’t held as tightly as those in the middle. So the gravity of the rest of the galaxy can pull some of them away. In fact, astronomers have identified a few dozen stars that appear to be escapees from M13. But the cluster also can grab stars from the space around it. One especially young star probably became a member of the cluster that way. And stars inside the cluster can change. Some of them merge, forming bright, blue stars that look much younger. And stars die. M13’s brightest member is dying right now. It’s about as massive as the Sun, but it’s puffed up to dozens of times the Sun’s diameter. Soon, it’ll blow away its outer layers, leaving only its tiny, dead core – one more change in an ancient family of stars. Script by Damond Benningfield

Three of the four big moons of Jupiter appear to have something in common: oceans of liquid water below their crusts. For Europa, the ocean is considered a slam dunk. The case is also strong for Ganymede. But the case for the third moon, Callisto, is the weakest. Callisto is about 3,000 miles in diameter – bigger than our own moon. And it’s more heavily cratered than any other large body in the solar system. That indicates that the surface of Callisto is pretty much dead. But things might be different far below the surface. In the 1990s, the Galileo spacecraft flew near Callisto eight times. Its measurements of the magnetic field around the moon hinted that a salty ocean was sloshing around inside. But those observations also could be produced by an electrically charged layer of Callisto’s thin atmosphere. In a recent study, though, scientists looked at all of Galileo’s observations, and used computer models to understand them. The work suggested that there is an ocean. It could be dozens of miles deep. But it’s buried beneath an icy crust that could be hundreds of miles thick. Two spacecraft that are en route to Jupiter will fly close to Callisto many times. Their observations should tell us for sure whether an ocean is sloshing below Callisto’s battered surface. Jupiter stands below our moon in the early evening twilight. It looks like a bright star. Script by Damond Benningfield

If stars had trophy cases, Vega’s would be packed. The leading light of Lyra was the first star other than the Sun to have its picture taken, the first to have its spectrum taken, and the first with a published measurement of its distance. Vega is impressive in many ways. It’s more than twice the size and mass of the Sun, and about 50 times the Sun’s brightness. It’s encircled by a wide belt of dust, produced by collisions between big chunks of ice and rock. In about 12,000 years, it’ll serve as the Pole Star. And in about 200,000 years it’ll become the brightest star in the night sky. Vega first had its picture taken in 1850. In 1872, an astronomer took a picture of its spectrum, spreading its light into its individual wavelengths. A spectrum reveals a star’s composition, motion, and much more. In 1838, Russian astronomer Friedrich von Struve published Vega’s parallax – the first publication for any star. He plotted its position when Earth was on opposite sides of the Sun. That revealed a tiny shift against the background of more-distant objects. That shift revealed a distance of about 26 light-years – just one light-year off the modern measurement. Vega is low in the east-northeast at nightfall and climbs high overhead during the night. It’s the fifth-brightest star in the night sky, so you can’t miss it – a beautiful star with a case full of trophies. Script by Damond Benningfield